1. Field of the Invention
The invention relates to a heat transfer system for controlling the temperature of a battery. More specifically, the invention relates to a method and apparatus useful in dissipating heat generated by operation of a battery used in, for example, a spacecraft or an electrical vehicle.
2. Brief Description of the Related Art
A battery includes one or more chargeable cells in which heat is generated as a result of normal operation. The cells and other electrical components of a battery are often temperature-sensitive and, therefore, control of the battery temperature is crucial to its safe and efficient operation. Typically, generated heat is dissipated from the cells of a battery via conductive heat transfer through a battery casing and thermal conductors which envelope the cells and other electrical components of the battery. Heat generated within the cell interconnects or electrodes is conducted away from cell terminals of the battery to the electrodes, from the electrodes across an electrical insulation gap to the cell case, and from the cell case to the battery case, and then to the heat sink (e.g., a radiator).
Dissipation of generated heat via the aforementioned route is convenient because each of the cell terminals, electrodes, and cell interconnects is a necessary electrical component of a battery regardless of how little heat must be dissipated. For a fifteen kilowatt spacecraft, the thermal conduction path external to the cell is used only for controlling the temperature of the battery and weighs about sixty pounds.
Conductive heat transfer via the aforementioned route is suitable in situations where the weight of the battery is not a concern. However, where the weight of the battery is a concern, the typical heat conduction paths impose restrictions on the use of the battery in certain applications. Such a weight restriction exists when a battery is used in a spacecraft where each unit of weight corresponds to an incremental unit of cost. For example, the cost to transport one pound of hardware into space is about $20,000 (1998 dollars). Thus, the benefits of any weight reduction would immediately result in a substantial cost savings.
In spacecraft, the battery is located immediately adjacent the heat sink to minimize the pathway to heat dissipation. For example, batteries in spacecraft are most often disposed at the periphery of the spacecraft such that the batteries may be in close thermal contact with an external radiator that dissipates heat into space. The design of spacecraft is somewhat limited in that as spacecraft become larger and are designed to employ more features requiring battery power, it becomes more difficult to effectively cool batteries not disposed at the periphery of the spacecraft. Difficulties include a lengthy and inefficient heat dissipation path, a need for additional cooling equipment, and the added weight that accompanies additional equipment. It is not always practical, nor always possible, to orient battery-powered features and, more importantly, the battery in close proximity to heat sinks located at the periphery of a spacecraft.
It would be desirable to provide an improved method of controlling and dissipating the heat generated by operation of a battery. Furthermore, it would be desirable to eliminate the necessity of a heavy thermal conductor within the battery, yet provide a suitable means for controlling and dissipating the heat generated within the battery. Additionally, it would be desirable to provide a weight-conservative apparatus capable of suitably controlling and dissipating the heat generated by operation of the battery. Still further, it would be desirable to provide a method and apparatus for cooling a battery remotely located with respect to a heat sink.